Renal vascular tone and reactivity is to be characterized from spectral analysis of recordings of pulsatile blood pressure otbained with micropuncture techniques. The pressure transmission characteristics of the vasculature will be used to estimate the dynamic mechanical properties of the blood vessel wall, its associated smooth muscle, and surrounding tissue. Thes properties will be estimated in normal rats both during control periods and following the administration of vasoacitve drugs. In addition, groups of both salt-sensitive and salt-resistant Dahl rats, maintained on a high salt diet for varying periods, will be studied in the same way in order to quantify changes in renal vascular tone and reactivity associated with the development of hypertension. Artificial pacemaker technology will be used to produce random excitation of the vasculature to permit dynamic compliance estimates to be obtained throughout the frequency band of physiological significance. An on-line microprocessor will be used for both data acqusition and analysis.